Wind Turbine Rotor Blade with Root, Main and Tip Sections

This application claims priority of European patent application no. 24 181 651.1, filed Jun. 12, 2024, the entire content of which is incorporated herein by reference.

The disclosure relates to a wind turbine rotor blade having a root section, a main section and a tip section. An outer end of the root section and an inner end of the main section are configured to be connected to one another, and an outer end of the main section and an inner end of the tip section are configured to be connected to one another.

Wind turbine rotor blades are configured for maximum annual energy production, which requires a maximum blade length. The ever-growing dimensions of wind turbine rotor blades are becoming more and more incompatible with the available transport solutions, in particular by road or by train. Dividing wind turbine rotor blades into a plurality of longitudinal segments has been suggested in view of the difficulties to transport a wind turbine rotor blade manufactured in one piece. However, an extremely strong connection between adjacent segments is necessary in order to withstand the extreme loads, including peak loads and fatigue loads. Many different connection techniques have been investigated and evaluated against criteria such as aerodynamic performance, added mass and dynamic loads, lightning protection, secondary fatigue effects, space requirements, manufacturing options, and practicality in the field.

How well a certain type of connection performs regarding these criteria is largely affected by the position of the connection, and the implications on the optimal position are often contradictory. For example, near the blade tip, less space is available for receiving the respective connector than is near the blade root. At the same time, negative impact on the aerodynamic performance may be more significant near the blade tip.

When considering the initial aim to facilitate transportation, still another perspective must be taken. This leads to a preference for blade segments of similar length.

A wind turbine rotor blade is disclosed for example in document EP 2 631 478 A1. The known blade includes three segments of roughly the same length.

It is an object of the disclosure to provide a wind turbine rotor blade offering a better compromise between simple construction and transportation requirements.

This object is solved by the wind turbine rotor blade by various embodiments of the disclosure.

A wind turbine rotor blade includes:

The wind turbine rotor blade may be configured for a wind turbine having a rotor with an essentially horizontal axis. The wind turbine may be operated at variable rotor speed and at varying pitch angles. To this end, the wind turbine rotor may include one or more of the wind turbine rotor blades mounted to a rotor hub via a pitch bearing, so that the pitch angle can be controlled with a pitch drive. Typically, the wind turbine rotor will have two or three wind turbine rotor blades.

The wind turbine rotor blade has a blade root adapted for being mounted to a wind turbine rotor hub, for example by a bolted connection to a pitch bearing. The blade root may have a circular cross-section.

The terms “inner end” and “outer end” refer to a radial position with reference to a rotor axis, “inner” means “closer to the rotor axis/closer to the blade root” and “outer” means “further away from the rotor axis/closer to the blade tip.” When the root section, the main section and the tip section are connected to each other, the three sections are aligned with a longitudinal axis of the wind turbine rotor blade. As the root section includes the blade root and the tip section includes the blade tip, all three sections together extend over the entire length of the complete wind turbine rotor blade.

The inner end of the tip section has a cross section shaped as an aerodynamic profile, which smoothly extends towards the blade tip, preferably over the entire tip section length. We note the tip section at its inner end may include connector which may extend in a direction towards the blade root, for example received in the main section when the main section and the tip section are connected to one another. The same applies to the main section, which at its outer end may include connector which extend in a direction towards the blade tip, for example received in the tip section. The feature on the cross sections of the outer end of the main section and of the inner end of the tip section being shaped as an aerodynamic profile refers to the cross sections of the wind turbine rotor blade when the main section and the tip section are connected to one another. The cross section of the outer end of the main section is arranged adjacent to or near the cross section of the inner end of the tip section, and both cross sections may be essentially identical, so that a smooth transition between the aerodynamic surfaces of the main section and the tip section is achieved.

Similar observations can be made with regard to the transition between the root section and the main section, whereas the cross sections of the outer end of the root section and the inner end of the main section are circular. The main section at its inner end may include connector which may extend in the direction towards the blade root, for example received in the root section when the root section and the main section are connected to one another. The same applies to the root section, which at its outer end may include connector which extend in the direction towards the blade tip, for example received in the main section. The cross sections of the outer end of the root section and of the inner end of the main section refer to the cross sections of the wind turbine rotor blade when the root section and the main section are connected to one another. The cross section of the outer end of the root section is arranged adjacent to or near the cross section of the inner end of the main section, and both cross sections may be essentially identical, so that a smooth transition between the outer surfaces of the root section and the main section is achieved. At this joint, however, this is less important than at the aerodynamically more relevant connection between the main section and the tip section, so that different diameters forming a step between the root section and the main section may be acceptable.

One of the advantages of the disclosure is that the connection between the root section and the main section due to the circular cross sections can be carried out in a very robust manner based on simple connection technology. Due to their circular cross sections, the outer end of the root section and the inner end of the main section will deform under load much less than if they had a more complex shape. In addition to the simplification achieved by the circular cross sections, the connection is also simple because it is located relatively close to the blade root, where the diameter is large and sufficient space is available. Added mass at this location also has relatively little influence on fatigue loads.

In an aspect, the root section has a circular cross section over its entire length. The diameter of the root section may be constant over the entire length, so that the root section has a simple, tubular shape. In the alternative, the diameter may vary over the root section length, such as in a smooth/continuous manner in a conical configuration, or possibly in a step-wise manner. In this aspect, the root section has a particularly simple configuration and can be manufactured at low costs.

In an aspect, the root section length is at least 5% of a total blade length. The root section length may be in a range of for example 5% to 20% of the total blade length, preferably in a range of 8% to 15% of the total blade length. In this aspect, the root section forms a substantial part of the wind turbine rotor blade.

In an aspect, the tip section length is the same as or smaller than the root section length and/or smaller than the main section length. In particular, the tip section length and the root section length can be selected such that the main section is the longest section, in particular longer than the root section and the tip section together. For example, the tip section length may be in a range of 5% to 20% of the total blade length and the root section length may be in a range of 5% to 20% of the total blade length. This leads to a main section length in a range of 60% to 90% of the total blade length, which is still very long, but may be manageable with respect to transportation. Remaining difficulties as to transportation of the main section may be outweighed by simple connection solutions: The connection between the root section and the main section is simplified by the circular cross section, as explained above, and the connection between the main section and the tip section is simplified by the fact that relatively low loads occur at the connection because the tip section is relatively short and lightweight.

In an aspect, the wind turbine rotor blade includes a spar cap and/or a shear web having an outer end, wherein the tip section length is selected such that the outer end of the spar cap and/or shear web is arranged within the main section and the tip section does not include a spar cap and/or shear web. This solution is appropriate in particular in combination with a tip section length in the range of 5% to 15% of the total blade length. Then, sufficient stability can be provided to the tip section by the blade shell, so that an additional reinforcing structure such as a spar cap and/or shear web is not required. The spar cap and/or shear web arranged in the main section may extend up to the outer end of the main section and may be connected to a connector used to form the connection with the tip section. However, the spar cap and/or shear web in the main section may also end in a distance from the outer end of the main section.

In further aspects, the tip section is manufactured as a single segment, the main section is manufactured as a single segment and/or the root section is manufactured as a single segment. “Manufactured as a single segment” means the respective segment is provided as a single part that cannot be disassembled into longitudinal sub-sections. The respective segment therefore must be transported in a single piece. Of course, the respective segment may have been assembled from different parts, for example by bonding two or more shell segments. In general, each of the sections may include any number of sub-segments. Manufacturing the respective section as a single segment avoids additional connections. In this regard, it is preferred to manufacture each of the three sections as a single segment, so that only two connections between adjacent segments are required.

In an aspect, the root section and the main section are connected via a different connection technology than the main section and the tip section. The different connection technologies, for example, a detachable connection or inseparable connection can be chosen according to the bearable loads and the installation space at the different connection areas. In another example, the different connection technologies can be a detachable connection for both joints, but being another technical principle, for example, a combination of a bolt connection having an intermediate connection piece and a bolt connection that connects the adjacent sections directly. In a further example, the different connection technologies can be an inseparable connection for both joints, but being another technical principle, for example, a combination of directly adhesively bonded sections and via an intermediate connection piece adhesively bonded sections.

In an aspect, the outer end of the root section and the inner end of the main section or the outer end of the main section and the inner end of the tip section are configured to be connected to one another by a detachable connection, in particular by a bolted connection. For maintenance or repair as well as for replacing one of the sections, the connection can be detached. With a bolted connection, this is particularly easy by loosening and/or removing the bolts and/or corresponding nuts. The bolted connection can be implemented similar to a bolted connection between a blade root and a rotor hub, if desired with bolts or bushings embedded in the inner and/or outer end of the main section and/or in the inner end of the tip section. A flange with a corresponding number of through-holes receiving one bolt each can be formed at the outer end of the root section.

In an aspect, the outer end of the main section and the inner end of the tip section are configured to be connected to one another by an inseparable connection, in particular by a glued connection. It is then not possible to detach the tip section once it has been connected to the main section, but the connection can be carried out at little added mass and requires less space than a detachable connection.

In further aspects, the tip section and/or the main section and/or the root section are made of a fiber reinforced material. In particular, a load carrying structure and/or shell parts of the respective section can be made of a fiber reinforced material. Proven manufacturing techniques can be used, for example a vacuum infusion process.

In a further aspect, the root section can be made of a metal material. In this case, the root section can be a one-part-section or be assembled from a plurality of metal components by welding and/or riveting. As mentioned above, the root section may be manufactured based on a fiber reinforced material, which usually offers a good compromise between strength, weight and costs. However, in particular when the root section is tubular or conical, a metal configuration has many advantages, in particular because a strong joint may be formed at the outer end of the root section based on a metal flange.

In an aspect, the wind turbine rotor blade includes a maximum chord located in the main section. This means the aerodynamically relevant portions of the rotor blade are placed in the main section (and also in the tip section), while the root section may not have an aerodynamic profile at all.

In an aspect, the wind turbine rotor blade includes a portion having a flatback profile. This portion can be arranged within the main section, in particular near the inner end of the main section. Seen in cross section, the flatback profile includes a flat portion at the trailing edge, the flat portion being arranged approximately perpendicular to a profile chord. In the tip section and in an outer part of the main section, an aerodynamic profile with a sharp trailing edge may be used.

In an aspect, the root section is assembled from at least two ring-shaped root segments. The at least two ring-shaped root segments may be connected with one other in a detachable or in an inseparable manner. Using two or more ring-shaped root segments allows to select a suitable number of segments to achieve the desired root section length.

The wind turbine rotor bladeofincludes a root sectionhaving a blade root, an outer endand a root section length, a main sectionhaving an inner end, an outer endand a main section length, and a tip sectionhaving an inner end, a blade tipand a tip section length. The wind turbine rotor bladehas a total blade lengthof 100 m, which is the sum of the root section lengthof 8 m, the tip section lengthof 8 m and the main section lengthof 84 m. The wind turbine rotor bladehas a leading edgeand a trailing edge.

The main sectionincludes a radial position where the wind turbine rotor bladehas its maximum chord. The wind turbine rotor bladehas two main spar caps, wherein the main spar capshown inis integrated into a pressure side shell member and the other main spar cap (not shown) is integrated into a suction side shell member. The main spar capsextend from the inner endof the main sectionto a radial position within the tip sectionnear the blade tip. In another embodiment not shown, a spar cap ends at the outer endof the main sectionand is not present in the tip section.

The main spar capsare arranged at or near a chordwise position where the aerodynamic profile of the wind turbinehas its maximum height. A second pair of spar capsextends over a central longitudinal part of the main sectiononly and is arranged at a chordwise position between the main spar capsand the trailing edge.

In, the outer endof the root sectionand the inner endof the

main sectionare connected one another. The outer endof the main sectionand the inner endof the tip sectionare connected to one another. Details on these connections will be explained with reference to.

shows an enlarged perspective view of the root sectionto the right. The root sectionhas a circular cross section over its entire length, in particular at the outer end. The inner endof the mains sectionhas a corresponding, circular cross section.

The root sectionof the rotor blade is made of a metal material, for example, steel. The blade rootof the root sectionis adapted to be connected to a wind turbine rotor hub via bolted connection (not shown). To this end, the blade rootis provided with a flange which is facing to the front side and cannot be seen in. The outer endof the root sectionis also provided with a flangewhich is facing inward and adapted to receive a number of boltslocked behind the flangeby nuts (not shown). The other ends of the boltsare received in a corresponding number of threaded bushings (not shown) which are embedded in the inner endof the main section. In this way, a strong and detachable connection is achieved.

The root sectionis manufactured as a single segment which includes four ring-shaped segments. The ring-shaped segmentsare steel components and are welded together to form the root section.

shows an alternative embodiment of the root section. Again, the root sectionhas a circular cross section over its entire length, in particular at the outer end. The inner endof the mains sectionhas a corresponding, circular cross section.

The root sectionof the rotor blade is made of a fiber reinforced plastic material, for example, glass fiber reinforced plastics. The blade rootof the root sectionis adapted to be connected to a wind turbine rotor hub via bolted connection. To this end, the blade rootis provided with a separate metal flange which is assembled at the front side between the blade rootand the rotor hub (not shown). Alternatively, the root sectioncan be assembled directly to the rotor hub.

The outer endof the root sectionis also provided with a flangewhich is facing inward. The flangeis assembled between the root sectionand the main section. It is adapted to receive a number of boltsfrom the root sectionand the main sectionlocked behind the flangeby nuts (not shown). The other ends of the boltsare received in a corresponding number of threaded bushings (not shown) which are embedded in the inner endof the main sectionand the outerof the root section. In this way, a strong and detachable connection is achieved.

shows an enlarged perspective view of the tip sectionto the left, and, further to the right, a part of the main sectionincluding its outer end. The outer endof the main sectionand the inner endof the tip sectioneach have a cross section shaped as an aerodynamic profile. The spar capis arranged in the main sectionand terminates close to the outer end.

A connector piecewhich also has a cross section shaped as an aerodynamic profile is adapted to be received with a first endin an opening within the outer endof the main sectionand with an opposing second endin an opening within the inner endof the tip section.

The first end, the second endand the corresponding openings in the outer endof the main sectionand in the inner endof the tip sectionare adapted to be connected by gluing to form a strong, inseparable connection.

It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.